Acceleration sensor and electronic apparatus

ABSTRACT

An acceleration sensor includes a base substrate provided with a first recess part, and a sensor part located on the first recess part and swingably supported in a depth direction of the first recess part by a support part, wherein the sensor part is sectioned into a first part and a second part by the support part, includes a movable electrode part in the first part and the second part, a through hole is provided at least at an end side in the second part larger in mass than the first part, and the base substrate includes a fixed electrode part in a position opposed to the movable electrode part in the first recessed part, and a second recess part deeper than the first recess part is provided in a position opposed to the end side of the sensor part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/420,323, filed May 23, 2019; which is a divisional of U.S. patentapplication Ser. No. 15/784,616, filed Oct. 16, 2017, now U.S. Pat. No.10,338,093, issued Jul. 2, 2019; which is a continuation of U.S. patentapplication Ser. No. 14/846,463, filed Sep. 4, 2015, now U.S. Pat. No.9,817,020, issued Nov. 14, 2017; which is a continuation of U.S.application Ser. No. 13/569,580, filed Aug. 8, 2012, now U.S. Pat. No.9,151,775, issued Oct. 6, 2015; which claims priority to Japanese PatentApplication No. 2011-178252, filed Aug. 17, 2011; all of which arehereby expressly incorporated by reference herein in their entireties.

BACKGROUND 1. Technical Field

The present invention relates to a physical quantity sensor and anelectronic apparatus including the physical quantity sensor.

2. Related Art

In related art, as a physical quantity sensor, an electrostaticcapacitance sensor in which a structure having a movable electrodesupported by a fixed part via an elastic element such as a torsionspring is formed, the movable electrode moves close to or away from afixed electrode in response to an acting external force or the like, andthereby, various physical quantities such as acceleration, angularvelocities, or the like may be detected by detecting the change inelectrostatic capacitance between the electrodes has been known.

As the electrostatic capacitance sensor, an ultracompact mechanicalacceleration sensor adapted to detect a physical quantity in a verticalaxis direction by a swing stage (mass part) swingably supported by atorsion rod (torsion spring) in a hollow space between two semiconductorwafers and swinging (displaced) like a seesaw due to an applied physicalquantity such as acceleration has been disclosed (for example, seePatent Document 1 (JP-A-9-189716)).

The ultracompact mechanical acceleration sensor (hereinafter, referredto as “acceleration sensor”) in Patent Document 1 is the electrostaticcapacitance sensor. Thereby, in the acceleration sensor, from thefollowing general expression (1) of the electrostatic capacitance, inorder to increase detection sensitivity, for example, the swing stage asa movable electrode and a first electrode as a fixed electrode opposedto the swing stage are made closer to increase the electrostaticcapacitance so that the electrostatic capacitance may change to anappreciable extent for small displacement of the swing stage and smallacceleration may be detected.

C=εS/d  (1)

(an electrostatic capacitance is C, an area of an opposed electrode isS, a distance between the opposed electrodes is d, permittivity is ε)

However, in the acceleration sensor, a surface of a first semiconductorwafer with the first electrode (fixed electrode) formed thereon is flatand the swing stage is formed like a flat plate.

Accordingly, in the acceleration sensor, for example, when the swingstage is displaced due to inertia force of the applied acceleration, thedisplacement may be suppressed by fluid resistance (squeeze filmdamping) of a gas existing between the swing stage and the surface ofthe first semiconductor wafer, and response may be slower and adetection range may be narrower.

Further, in the acceleration sensor, the swing stage maybe stuck to thesurface of the first semiconductor wafer due to charging caused bystatic electricity.

SUMMARY

An advantage of some aspects of the invention is to solve at least apart of the problems described above, and the invention can beimplemented as the following embodiments or application examples.

APPLICATION EXAMPLE 1

A physical quantity sensor according to this application exampleincludes a base substrate provided with a first recess part, and asensor part located on the first recess part and swingably supported ina depth direction of the first recess part by a support part extendingin a direction of a first axis, wherein the sensor part is sectionedinto a first part and a second part by the support part, includes amovable electrode part in the first part and the second part, the secondpart is larger in mass than the first part, and a through hole isprovided at least in one of the first part and the second part, and thebase substrate includes a fixed electrode part in a position overlappingwith the movable electrode part in a plan view, and a second recess partdeeper than the first recess part is provided in a position overlappingwith an end of the sensor part in the plan view.

According to the configuration, in the physical quantity sensor, thethrough hole is provided at the end side of the second part of thesensor part, and the second recess part deeper than the first recesspart is provided in a part opposed to the end side of the second part ofthe sensor part in the base substrate.

Thereby, in the physical quantity sensor, for example, when the secondpart of the sensor part swings (is displaced) in a direction closer to abottom surface of the first recess part around the support part(rotation center) due to inertia force of applied acceleration, flowresistance of a gas existing between the second part of the sensor partand the bottom surface of the first recess part may be reduced comparedto the case without the through hole or the second recess part.

As a result, in the physical quantity sensor, for example, displacementof the sensor part by application of acceleration becomes smoother, andthus, response becomes faster and a detection range may be made broader.

Further, in the physical quantity sensor, the mass of the second part ofthe sensor part is larger (heavier) than that of the first part, andthus, the sensor part is not balanced between the first part and thesecond part, and, for example, the sensor part may be efficientlydisplaced (rotated) in response to the acceleration applied to thesensor part.

As a result, in the physical quantity sensor, detection sensitivity atapplication of acceleration may be further improved.

APPLICATION EXAMPLE 2

In the physical quantity sensor according to the application example, itis preferable that a conducting part is provided within the secondrecess part, and the conducting part is connected to the movableelectrode part.

According to the configuration, in the physical quantity sensor, theconducting part is provided within the second recess part and theconducting part and the movable electrode part are connected, and thus,for example, charge generated when the sensor part is processed byreactive ion etching or the like may be let out from the base substrateside to the sensor substrate side via the conducting part.

As a result, in the physical quantity sensor, sticking of the sensorpart to the base substrate due to charging may be avoided.

APPLICATION EXAMPLE 3

In the physical quantity sensor according to the application example, itis preferable that a plurality of the through holes are provided alongthe direction of the first axis.

According to the configuration, in the physical quantity sensor, theplural through holes are arranged in strip shapes in the direction ofthe first axis, and thus, compared to other shapes, internal spaces ofthe respective through holes may be made larger while the mass of thesensor part is secured.

As a result, in the physical quantity sensor, flow resistance of a gasexisting between the second part of the sensor part and a bottom surfaceof the second recess part may be further reduced.

Therefore, in the physical quantity sensor, for example, thedisplacement of the sensor part by application of acceleration becomeseven smoother, and thus, the response becomes faster and the detectionrange may be further improved.

APPLICATION EXAMPLE 4

In the physical quantity sensor according to the application example, itis preferable that the first recess part is provided so that an air gapbetween the sensor part and itself may be larger from the support partof the sensor part toward the end.

According to the configuration, in the physical quantity sensor, thefirst recess part is provided so that the air gap between the sensorpart and itself may be larger from the support part side of the sensorpart toward the end side, and thus, at the support part side with thesmaller displacement of the sensor part, the air gap between the bottomsurface of the first recess part and the sensor part may be made smallerand, at the end side with the larger displacement of the sensor part,the air gap between the bottom surface of the first recess part and thesensor part may be made larger.

As a result, in the physical quantity sensor, the detection sensitivitymay be improved than in the case where the bottom surface of the firstrecess part is formed by a flat surface with reference to the air gapbetween the end side with the larger displacement of the sensor part anditself.

APPLICATION EXAMPLE 5

In the physical quantity sensor according to the application example, itis preferable that an insulating material is used for the basesubstrate, and a semiconductor material is used for the sensor part.

According to the configuration, in the physical quantity sensor, theinsulating material is used for the base substrate and the semiconductormaterial is used for the sensor part, and thus, insulation and isolationbetween the base substrate and the sensor part may be easily performedby the insulating material.

In addition, in the physical quantity sensor, by using low-resistancesilicon, for example, as the semiconductor material for the sensor part,the sensor part and the movable electrode part may be integrated.

Thereby, in the physical quantity sensor, the movable electrode part maybe easily provided in the sensor part.

APPLICATION EXAMPLE 6

An electronic apparatus according to the application example includesthe physical quantity sensor according to any one of the applicationexamples.

Accordingly, the electronic apparatus having the configuration includesthe physical quantity sensor according to any one of the applicationexamples, and thus, the electronic apparatus that exerts the effectsaccording to any one of the application examples may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic perspective view showing a general configurationof an acceleration sensor of a first embodiment.

FIGS. 2A and 2B are schematic plan and sectional views of theacceleration sensor in FIG. 1, and FIG. 2A is a plan view and FIG. 2B isa sectional view along an A-A line in FIG. 2A.

FIG. 3 is a schematic sectional view for explanation of an operation ofthe acceleration sensor.

FIGS. 4A and 4B are schematic sectional views for explanation ofsticking of a sensor part, and FIG. 4A is a sectional view showing thecase without a conducting part and FIG. 4B is a sectional view showingthe case with the conducting part.

FIGS. 5A and 5B are schematic plan and sectional views showing a generalconfiguration of an acceleration sensor of a second embodiment, and FIG.5A is a plan view and FIG. 5B is a sectional view along an A-A line inFIG. 5A.

FIG. 6 is a perspective view of an electronic apparatus (notebookpersonal computer) including the acceleration sensor.

FIG. 7 is a perspective view of an electronic apparatus (cellular phone)including the acceleration sensor.

FIG. 8 is a perspective view of an electronic apparatus (digital stillcamera) including the acceleration sensor.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

As below, embodiments of the invention will be explained with referenceto the drawings. In the following respective drawings, for convenienceof explanation, dimension ratios of the respective component elementsare different from actual dimension ratios.

First Embodiment

First, an acceleration sensor as an example of a physical quantitysensor according to a first embodiment will be explained. Theacceleration sensor may detect acceleration in a Z-axis direction(thickness direction).

FIG. 1 is a schematic perspective view showing a general configurationof the acceleration sensor of the first embodiment. FIGS. 2A and 2B areschematic plan and sectional views of the acceleration sensor in FIG. 1,and FIG. 2A is a plan view and FIG. 2B is a sectional view along an A-Aline in FIG. 2A.

As shown in FIGS. 1, 2A, and 2B, an acceleration sensor 1 includes abase substrate 10 and a sensor substrate 20.

The base substrate 10 has a nearly rectangular planar shape, and a firstrecess part 11 having a nearly rectangular planar shape is provided in acenter part. It is preferable that an insulating material such as glassis used for the base substrate 10. For example, for the base substrate10, glass containing alkali metal ions (movable ions) (for example,borosilicate glass such as Pyrex (registered trademark) glass) ispreferably used.

Note that, for the base substrate 10, a high-resistance silicon materialmay be used.

The sensor substrate 20 has a nearly rectangular planar shape, and isbonded to a principal surface 10 a on which the first recess part 11 ofthe base substrate 10 is provided.

The sensor substrate 20 includes a sensor part 21 having a nearlyrectangular planar shape provided above the first recess part 11 of thebase substrate 10, a frame part 22 having a frame shape surrounding thesensor part 21, and a pair of support parts 23 a, 23 b having beamshapes connecting the sensor part 21 and the frame part 22. Note thatthe frame part 22 is unnecessary when the support parts 23 a, 23 b arebonded to the base substrate 10 for reliable support of the sensor part21.

The sensor part 21 is swingably supported in the depth direction (Z-axisdirection) of the first recess part 11 by the support parts 23 a, 23 b.Specifically, the sensor part 21 is rotatably supported like a seesaw inthe Z-axis direction by torsion of the support parts 23 a, 23 b withinan elastic deformation range (torsion spring action) around an axis lineB passing through the support parts 23 a, 23 b.

The sensor part 21 is sectioned by the support parts 23 a, 23 b (axisline B) into a first part 21A at the −X side and a second part 21B atthe +X side.

The sensor part 21 has a movable electrode part at the side opposed tothe first recess part 11 of the base substrate 10 of the first part 21Aand the second part 21B.

In the sensor part 21, masses are different between the first part 21Aand the second part 21B. Specifically, the second part 21B is formedlonger in length in the X-axis direction than the first part 21A.Further, through holes 24 penetrating in the Z-axis direction are formedat least at the end side in the second part 21B having the larger massthan that of the first part 21A. Note that, in the embodiment, thethrough holes 24 are formed in the entire range of the sensor part 21.

The through holes 24 are formed in strip shapes (elongated rectangularshapes) extending in the extension direction (Y-axis direction) of thesupport parts 23 a, 23 b. The plural through holes 24 are arranged inthe X-axis direction as the width direction of the strips.

It is preferable that a semiconductor material such as low-resistancesilicon is used for the sensor substrate 20.

Thereby, in the acceleration sensor 1, the movable electrode part andthe sensor part 21 are integrated (the entire sensor part 21 is themovable electrode part).

The base substrate 10 has fixed electrode parts 12, 13 in positionsopposed to the movable electrode part of the first part 21A and thesecond part 21B of the sensor part 21 in the first recess part 11. Thefixed electrode parts 12, 13 have nearly rectangular planar shapes andequal areas to each other, and have line symmetric shapes with respectto the support parts 23 a, 23 b (axis line B) in the plan view.

Note that the plural through holes 24 of the sensor part 21 are arrangedin line symmetric shapes with respect to the support parts 23 a, 23 b(axis line B) in the plan view in parts opposed to the fixed electrodeparts 12, 13. Thereby, the acceleration sensor 1 is adapted so that theopposed areas of the movable electrode part and the fixed electrodeparts 12, 13 may be equal in the first part 21A and the second part 21Bof the sensor part 21.

On the base substrate 10, a second recess part 14 having a nearlyrectangular planar shape is provided in contact with the first recesspart 11 in a part nearer the end (+X direction) of the second part 21Bof the sensor part 21 than the fixed electrode part 13 and opposed tothe end side of the second part 21B of the sensor part 21.

Here, a depth D2 from the principal surface 10 a to a bottom surface 14a of the second recess part 14 is deeper than a depth D1 from theprincipal surface 10 a to a bottom surface 11 a of the first recess part11 (D2>D1).

A conducting part 15 having a nearly rectangular planar shape isprovided on the bottom surface 14 a of the second recess part 14, andthe conducting part 15 is connected to the movable electrode part of thesensor part 21 via wiring (not shown) (also connected to the frame part22 of the sensor substrate 20 connected to the movable electrode part).Note that the conducting part 15 and the fixed electrode parts 12, 13are electrically independently formed from each other.

In FIGS. 1, 2A, and FIG. 5A, which will be described later, the fixedelectrode parts 12, 13 and the conducting part 15 are hatched forconvenience of explanation.

Constituent materials of the fixed electrode parts 12, 13 and theconducting part 15 are not particularly limited as long as they haveconductivity, but various electrode materials may be used. Specifically,for example, oxides (transparent electrode materials) such as ITO(Indium Tin Oxide), IZO (Indium Zinc Oxide), In₃O₃, SnO₂, Sb-containingSnO₂, and Al-containing ZnO, Au, Pt, Ag, Cu, Al or alloys containing themetals, etc. are cited, and one or more of them may be combined for use.

A forming method (depositing method) of the fixed electrode parts 12, 13and the conducting part 15 is not particularly limited, but, forexample, vacuum evaporation, sputtering (low-temperature sputtering),dry plating such as ion plating, wet plating such as electrolyticplating or non-electrolytic plating, thermal spraying, thin-filmbonding, or the like may be cited.

For shape formation of the base substrate 10 and the sensor substrate20, technologies of photolithography and etching are used, and, byperforming vertical etching using reactive ion etching (RIE) or thelike, for example, inner wall surfaces of the first recess part 11 andthe second recess part 14 of the base substrate 10, side surfaces of thesensor part 21, and inner surfaces of the through holes 24 are formed tobe perpendicular to a principal surface of the sensor part 21.

As the reactive ion etching, for example, a processing method using anetching device including inductively coupled plasma (ICP) may be used.

In the acceleration sensor 1, glass containing alkali metal ions(movable ions) (for example, borosilicate glass such as Pyrex(registered trademark) glass) is used for the base substrate 10 and asilicon material is used for the sensor substrate 20, and thereby, theymay be bonded by anodic bonding (a method of bringing the base substrate10 and the sensor substrate 20 into close contact, applying a voltage ofabout 1 KV under a temperature of about 400° C., generating anelectrostatic attractive force near a boundary face between them, andbonding them by covalent bonding).

Here, an operation of the acceleration sensor 1 will be explained.

FIG. 3 is a schematic sectional view for explanation of the operation ofthe acceleration sensor showing a state in which acceleration as aphysical quantity is applied in the Z-axis direction.

As shown in FIG. 3, in the acceleration sensor 1, for example, whenacceleration G is applied in the +Z-axis direction orthogonal to theprincipal surface of the sensor part 21, the sensor part 21 rotates likea seesaw around the axis line B due to inertia force and tilts withrespect to the base substrate 10.

Specifically, in the acceleration sensor 1, the first part 21A of thesensor part 21 moves away from the fixed electrode part 12 and thesecond part 21B of the sensor part 21 moves closer to the fixedelectrode part 13.

In this regard, an air gap Si between the fixed electrode part 12 andthe first part 21A (movable electrode part) of the sensor part 21becomes larger and an air gap S2 between the fixed electrode part 13 andthe second part 21B (movable electrode part) of the sensor part 21becomes smaller, and thus, the electrostatic capacitance between thefirst part 21A and the fixed electrode part 12 becomes smaller and theelectrostatic capacitance between the second part 21B and the fixedelectrode part 13 becomes larger.

Therefore, in the acceleration sensor 1, by obtaining a voltage waveformby C-V conversion from the difference (differential capacitance) betweenthe electrostatic capacitance generated in the air gap S1 between thefirst part 21A of the sensor part 21 and the fixed electrode part 12 andthe electrostatic capacitance generated in the air gap S2 between thesecond part 21B of the sensor part 21 and the fixed electrode part 13,the acceleration applied to the acceleration sensor 1 may be detected.

In this regard, when the sensor part 21 rotates, internal spaces of theplural through holes 24 of the sensor part 21 respectively serve aschannels for a gas (for example, the air or an inert gas such asnitrogen, helium, or argon) existing in the air gap S1 or the air gap S2to flow.

Thereby, when the sensor part 21 rotates, the acceleration sensor 1 maylet the gas existing in the air gap S1 or the air gap S2 out through theplural through holes 24.

In addition, in the acceleration sensor 1, the second recess part 14deeper than the first recess part 11 is provided in the part nearer theend (+X direction) of the second part 21B of the sensor part 21 than thefixed electrode part 13 in the base substrate 10 and opposed to the endside of the second part 21B of the sensor part 21.

Thereby, in the acceleration sensor 1, when the sensor part 21 rotates,the degree of compression of a gas existing between the end side of thesecond part 21B of the sensor part 21 and the bottom surface 14 a of thesecond recess part 14 is relaxed (becomes lower) compared to the casewithout the second recess part 14 (the case with the first recess part11 only).

Accordingly, in the acceleration sensor 1, the flow resistance of thegas existing between the end side of the second part 21B of the sensorpart 21 and the bottom surface 14 a of the second recess part 14 isreduced.

As a result, in the acceleration sensor 1, displacement (rotation) ofthe sensor part 21 by application of acceleration becomes smoother.

As described above, in the acceleration sensor 1 of the firstembodiment, the through holes 24 are formed at least at the end side ofthe second part 21B of the sensor part 21, and the second recess part 14deeper than the first recess part 11 is provided in the part opposed tothe end side of the second part 21B of the sensor part 21 in the basesubstrate 10.

Thereby, in the acceleration sensor 1, for example, when the second part21B of the sensor part 21 is displaced around the rotation center of thesupport parts 23 a, 23 b (axis line B) due to the inertia force of theapplied acceleration, the flow resistance of a gas existing between thesecond part 21B of the sensor part 21 and the bottom surface 11 a of thefirst recess part 11 and the bottom surface 14 a of the second recesspart 14 is reduced compared to the case without the through holes 24 orthe second recess part 14.

As a result, in the acceleration sensor 1, the displacement of thesensor part 21 by application of acceleration becomes smoother, andthus, the detection range of the acceleration may be made broader.

Further, in the acceleration sensor 1, the mass of the second part 21Bof the sensor part 21 is larger (heavier) than that of the first part21A, and thus, the sensor part 21 is not balanced between the first part21A and the second part 21B, and the sensor part 21 may be efficientlyrotated in response to the acceleration applied to the sensor part 21.

As a result, in the acceleration sensor 1, the detection sensitivity atapplication of acceleration may be further improved.

Furthermore, in the acceleration sensor 1, the through holes 24 of thesensor part 21 are formed in strip shapes (elongated rectangular shapes)extending in the extension direction (Y-axis direction) of the supportparts 23 a, 23 b and the plural through holes 24 are arranged in thewidth direction (X-axis direction) of the strips, and thus, compared toother shapes, the internal spaces of the respective through holes 24maybe made larger while the mass of the sensor part 21 is secured.

As a result, in the acceleration sensor 1, when the sensor part 21rotates, the flow resistance of the gas existing between the second part21B of the sensor part 21 and the bottom surface 11 a of the firstrecess part 11 and the bottom surface 14 a of the second recess part 14may be further reduced.

Therefore, in the acceleration sensor 1, the displacement of the sensorpart 21 by application of acceleration becomes even smoother, and thus,the detection range of the acceleration may be further improved.

In addition, in the acceleration sensor 1, the conducting part 15 isprovided within the second recess part 14 and the conducting part 15 andthe movable electrode part (the frame part 22 of the sensor substrate 20connected to the movable electrode part) are connected, and thus, forexample, charge generated when the sensor substrate 20 including thesensor part 21 is processed by reactive ion etching or the like may belet out from the base substrate 10 side to the sensor substrate 20 sidevia the conducting part 15.

As a result, in the acceleration sensor 1, sticking of the sensor part21 to the base substrate 10 due to charging may be avoided.

Here, using the drawings, sticking of the sensor part 21 will bedescribed in detail. FIGS. 4A and 4B are schematic sectional views forexplanation of sticking of the sensor part, and FIG. 4A is a sectionalview showing the case without a conducting part and FIG. 4B is asectional view showing the case with the conducting part as in theembodiment.

As shown in FIG. 4A, in the case where the conducting part 15 is notprovided on the base substrate 10, when the sensor part 21 is formed byprocessing the sensor substrate 20 using silicon by reactive ion etchingor the like, charge is accumulated at the base substrate side and apotential difference is generated between the sensor part 21 and thebase substrate 10. Thereby, without the conducting part 15, the sensorpart 21 may stick to the base substrate 10.

On the other hand, as shown in FIG. 4B, in the embodiment, the sensorpart 21 is formed by reactive ion etching or the like under thecondition that the conducting part 15 provided within the second recesspart 14 of the base substrate 10 and the sensor substrate 20 areelectrically connected to each other (specifically, the wiring extendingfrom the conducting part 15 to the principal surface 10 a is in contactwith the part to be the frame part 22 of the sensor substrate 20).

Thereby, in the embodiment, the charge generated at reactive ion etchingmay be let out from the base substrate 10 side to the sensor substrate20 side via the conducting part 15.

As a result, in the embodiment, charge accumulation at reactive ionetching may be reduced and, when the sensor part 21 is formed, thesensor part 21 and the base substrate 10 (conducting part 15) are at thesame potential and sticking of the sensor part 21 to the base substrate10 may be avoided.

Further, in the acceleration sensor 1, the glass such as borosilicateglass is used for the base substrate 10 and the semiconductor materialsuch as silicon is used for the sensor part 21, and thus, insulation andisolation between the base substrate 10 and the sensor part 21 may beeasily performed by the glass having an insulation property.

In addition, in the acceleration sensor 1, by using the low-resistancesilicon as the semiconductor material for the sensor part 21, the sensorpart 21 and the movable electrode part may be integrated.

Thereby, in the acceleration sensor 1, the movable electrode part may beeasily provided in the sensor part 21.

Second Embodiment

Next, an acceleration sensor according to a second embodiment will beexplained. In the acceleration sensor of the second embodiment, theabove described first recess part of the acceleration sensor of thefirst embodiment is formed in a step-like shape.

FIGS. 5A and 5B are schematic plan and sectional views showing a generalconfiguration of the acceleration sensor of the second embodiment, andFIG. 5A is a plan view and FIG. 5B is a sectional view along an A-A linein FIG. 5A. Note that the parts in common with the first embodiment havethe same signs and their detailed explanation will be omitted and theparts different from the first embodiment will be centered forexplanation.

As shown in FIGS. 5A and 5B, in an acceleration sensor 2, a first recesspart 111 of the base substrate 10 is formed in a step-like shape so thatan air gap between the sensor part 21 and itself maybe larger from thesupport parts 23 a, 23 b (axis line B) side of the sensor part 21 towardthe end side.

Specifically, in the acceleration sensor 2, a bottom surface 111 a and abottom surface 111 b of the first recess part 111 are formed to have adifference in level so that an air gap between the bottom surface 111 bof the first recess part 111 and the sensor part 21 at the support parts23 a, 23 b (axis line B) side may be smaller than an air gap between thebottom surface 111 a of the first recess part 111 and the sensor part 21at the end side.

In other words, in the acceleration sensor 2, a depth D3 from theprincipal surface 10 a of the base substrate 10 to the bottom surface111 b of the first recess part 111 is shallower than the depth D1 fromthe principal surface 10 a of the base substrate 10 to the bottomsurface 111 a of the first recess part 111 (D3<D1).

Accordingly, in the acceleration sensor 2, at the support parts 23 a, 23b side with the smaller displacement of the sensor part 21 rotating likea seesaw, the air gap (D3) between the bottom surface 111 b of the firstrecess part 111 and the sensor part 21 may be made smaller and, at theend side with the larger displacement of the sensor part 21, the air gap(D1) between the bottom surface 111 a of the first recess part 111 andthe sensor part 21 may be made larger.

As a result, in the acceleration sensor 2, the electrostaticcapacitances between the sensor part 21 (movable electrode part) and thefixed electrode parts 12, 13 may be made larger than in the case wherethe bottom surface 111 b of the first recess part 111 is formed by aflat surface (bottom surface 111 a) with reference to the air gap (D1)between the end side with the larger displacement of the sensor part 21and itself (D3=D1), and thus, compared to the first embodiment, thedetection sensitivity may be further improved.

Note that, in FIGS. 5A and 5B, the fixed electrode parts 12, 13 areintegrally provided respectively from the bottom surface 111 a to thebottom surface 111 b, however, they may be divisionally provided intoparts of the bottom surface 111 a and parts of the bottom surface 111 b.

Thereby, in the acceleration sensor 2, detection errors of theelectrostatic capacitances in the step parts that may occur in the casewhere the fixed electrode parts 12, 13 are respectively integrated maybe avoided, and thus, changes in the electrostatic capacitance may bedetected with high accuracy.

Note that the first recess part 111 of the base substrate 10 may beformed in a slope shape in place of the step-like shape, and may exertthe same effects as those described above.

Third Embodiment

Next, an electronic apparatus including the acceleration sensors of therespective embodiments according to a third embodiment will beexplained.

FIG. 6 is a perspective view showing a configuration of a mobile (ornotebook) personal computer as an electronic apparatus including theacceleration sensor.

As shown in FIG. 6, a personal computer 1100 includes a main body unit1104 having a keyboard 1102 and a display unit 1106 having a displaypart 100, and the display unit 1106 is rotatably supported via a hingestructure part with respect to the main body unit 1104.

The personal computer 1100 contains the acceleration sensor 1.

Note that the personal computer 1100 may contain the acceleration sensor2 in place of the acceleration sensor 1.

FIG. 7 is a perspective view showing a configuration of a cellular phone(including PHS) as an electronic apparatus including the accelerationsensor.

As shown in FIG. 7, a cellular phone 1200 includes plural operationbuttons 1202, an ear piece 1204, and a mouthpiece 1206, and a displaypart 100 is provided between the operation buttons 1202 and the earpiece 1204.

The cellular phone 1200 contains the acceleration sensor 1.

Note that the cellular phone 1200 may contain the acceleration sensor 2in place of the acceleration sensor 1.

FIG. 8 is a perspective view showing a configuration of a digital stillcamera as an electronic apparatus including the acceleration sensor. InFIG. 8, also connection to an external device is simply shown.

Here, in a typical camera, a silver halide photographic film is exposedto light by an optical image of a subject, on the other hand, a digitalstill camera 1300 photoelectrically converts an optical image of asubject using an image sensing device such as a CCD (Charge CoupledDevice) and generates imaging signals (image signals).

On a back surface (on the front side in the drawing) of a case (body)1302 in the digital still camera 1300, a display part 1310 is providedand adapted to display based on the imaging signals by the CCD, and thedisplay part 1310 functions as a finder that displays the subject as anelectronic image.

Further, on the front side (the back side in the drawing) of the case1302, a light receiving unit 1304 including an optical lens (imagingsystem), the CCD, etc. is provided.

When a photographer checks a subject image displayed on the display part1310 and presses down a shutter button 1306, the imaging signals of theCCD at the time are transferred and stored in a memory 1308.

Further, in the digital still camera 1300, a video signal outputterminal 1312 and an input/output terminal for data communication 1314are provided on a side surface of the case 1302. Furthermore, atelevision monitor 1430 is connected to the video signal output terminal1312 and a personal computer 1440 is connected to the input/outputterminal for data communication 1314, respectively, according to need.In addition, by predetermined operation, the imaging signals stored inthe memory 1308 are output to the television monitor 1430 and thepersonal computer 1440.

The digital still camera 1300 contains the acceleration sensor 1.

Note that the digital still camera 1300 may contain the accelerationsensor 2 in place of the acceleration sensor 1.

The electronic apparatus having the configuration includes theacceleration sensor 1 or the acceleration sensor 2, and thus, may be anadvantageous electronic apparatus that exerts the effects described inthe respective embodiments.

The electronic apparatus including the acceleration sensor may beapplied not only to the personal computer (mobile personal computer) inFIG. 6, the cellular phone in FIG. 7, and the digital still camera inFIG. 8 but also to an inkjet ejection device (for example, an inkjetprinter), a laptop personal computer, a television, a video camera, avideo tape recorder, various navigation systems, a pager, a personaldigital assistance (with or without communication function), anelectronic dictionary, a calculator, an electronic game machine, a wordprocessor, a work station, a videophone, a security television monitor,electronic binoculars, a POS terminal, medical devices (for example, anelectronic thermometer, a sphygmomanometer, a blood glucose meter, anelectrocardiographic measurement system, an ultrasonic diagnosticsystem, an electronic endoscope), a fish finder, various measurementinstruments, meters and gauges (for example, meters for vehicles,airplanes, and ships), a flight simulator, etc.

What is claimed is:
 1. An acceleration sensor comprising: three mutuallyorthogonal axes being defined as an X-axis, a Y-axis, and a Z-axis; abase substrate made of glass, the base substrate including: a recess;first and second fixed electrodes arranged along the X-axis; and aconductor disposed on a bottom of the recess; a sensor member, thesensor member being configured with: a first member facing the firstfixed electrode via a first gap along the Z-axis; a second member facingthe second fixed electrode via a second gap along the Z-axis, the secondmember having a larger mass than the first member; and a swing axis thatextends along the Y-axis, the swing axis being located between the firstmember and the second member, the sensor member being swingable withrespect to the swing axis, wherein an edge portion of the second memberoverlaps with the conductor in a plan view along the Z-axis, and theedge portion is located at an opposite side of the second member withrespect to the swing axis in a direction along the X-axis, the edgeportion has: first, second, and third sides in the plan view; the firstside extends along the Y-axis; the second and third sides extend alongthe X-axis; the second side is connected to one end of the first side;and the third side is connected to the other end, which is opposite tothe one end, of the first side, the conductor has: first, second, andthird ends in the plan view, the first, second, and third ends arelocated at positions corresponding to the first, second, and third sidesof the edge portion, respectively, in the plan view; the first end islocated outwardly away from the first side of the edge portion along theX-axis in the plan view; the second end is located outwardly away fromthe second side of the edge portion along the Y-axis in the plan view;and the third end is located outwardly away from the third side of theedge portion along the Y-axis in the plan view, and the sensor member ismade of a low-resistance silicon material.
 2. The acceleration sensoraccording to claim 1, wherein the first fixed electrode is configured todetect a first electrostatic capacitance between the first member of thesensor member and the first fixed electrode, and the second fixedelectrode is configured to detect a second electrostatic capacitancebetween the second member of the sensor member and the second fixedelectrode.
 3. The acceleration sensor according to claim 2, wherein thebase substrate is made of an insulating material.
 4. The accelerationsensor according to claim 3, wherein the conductor is electricallyconnected to the sensor member.
 5. The acceleration sensor according toclaim 4, wherein the conductor is electrically independent from thefirst and second fixed electrodes.
 6. The acceleration sensor accordingto claim 5, wherein each of the first and second fixed electrodes hasfirst and second edges opposite to each other along the Y-axis, and eachof the first and second members of the sensor member has first andsecond edges opposite to each other along the Y-axis, the first edge ofthe first fixed electrode is located outwardly away from the first edgeof the first member of the sensor member along the Y-axis in the planview, and the second edge of the first fixed electrode is locatedoutwardly away from the second edge of the first member of the sensormember along the Y-axis in the plan view, and the first edge of thesecond fixed electrode is located outwardly away from the first edge ofthe second member of the sensor member along the Y-axis in the planview, and the second edge of the second fixed electrode is locatedoutwardly away from the second edge of the second member of the sensormember along the Y-axis in the plan view.
 7. The acceleration sensoraccording to claim 6, further comprising: first and second supports thatsupport the sensor member, the first and second supports extending alongthe Y-axis direction, wherein the swing axis passes through the firstand second supports in the plan view.
 8. An electronic apparatuscomprising the acceleration sensor according to claim
 1. 9. Anelectronic apparatus comprising the acceleration sensor according toclaim
 2. 10. An electronic apparatus comprising the acceleration sensoraccording to claim
 3. 11. An electronic apparatus comprising theacceleration sensor according to claim
 4. 12. An electronic apparatuscomprising the acceleration sensor according to claim
 5. 13. Anelectronic apparatus comprising the acceleration sensor according toclaim
 6. 14. An electronic apparatus comprising the acceleration sensoraccording to claim 7.